The present invention relates generally to surgical methods and apparatus, and in particular, to methods and apparatus for bone positioning during surgery.
An important aspect of certain types of surgery, particularly arthroplastic surgery, is proper bone positioning. Bone positioning involves proper selection and implantation of a prosthetic component such that it does not change the natural posture and attitude of the remaining bones.
By way of example, total hip replacement surgery requires appropriate selection of the hip prosthesis to avoid changing the overall length and lateral offset of the leg. Unequal leg length and/or lateral offset can undesirably result in a persistent limp in the patient. However, if a hip prosthesis having the correct dimensions is selected, then appropriate leg length and lateral offset may be accomplished.
A general technique that facilitates the selection of an appropriately-sized prosthetic involves performing a reference measurement prior to the hip replacement, and then adjusting the size of the prosthetic until the reference measurement can be reproduced. Once the size of the prosthetic results in a measurement that is largely identical to the initial reference measurement, then a prosthetic of that size is employed within the patient.
Many methods of performing bone positioning measurements have been developed. Most of these methods employ a reference pin that is implanted into the patient""s ilium. Another device is then used to measure the length from the implanted pin to a reference point on the femur. For example, U.S. Pat. No. 6,027,507 to Anderson et al. shows a leg length gauge that employs a pin attached to a patient""s ilium and a second pin attached to the patient""s femur. The gauge includes two vertical rods that fit on top of the pins, and a horizontal rod that is secured to the two vertical rods. The length between the two vertical rods may be adjusted to accommodate the distance between the two pins by sliding the horizontal rod with respect to one of the vertical rods. Once adjusted to the appropriate length, the two vertical rods should fit on the two pins in the ilium and femur. The vertical rods and horizontal rod are removed as a unit, retaining the appropriate length measurement. After replacement of the hip, the rod assembly is placed over the pins. If the vertical rods do not fit, then an adjustment in the prosthetic fit or length is indicated. If the vertical rods fit over the pins, then the prosthetic size is correct.
Other prior art patents, including U.S. Pat. No. 5,814,050 to Benson and U.S. Pat. No. 5,122,145 to Fishbane use similar devices that rely upon measuring the distance between reference pins in the ilium and the femur. However, the above cited prior art patents suffer from various shortcomings that limit their usefulness in bone positioning during total hip replacement surgery. For example, many of the techniques and devices taught in those patents are difficult to use because, among other things, they require the placement of multiple bone pins. Such devices also present difficulties in aligning the measurement device.
In addition, many prior art devices, including some of the devices identified above, measure only length, and do not adequately measure lateral offset. The failure to provide reliable lateral offset measurements can result in improper final bone positioning after implantation of the prosthesis.
One prior art device shown in U.S. Pat. No. 6,193,724 to Chan (the xe2x80x9cChan devicexe2x80x9d) addresses some of the above needs through the use of an adjustable outrigger device and an anchor pin that is attached to the ilium. The adjustable outrigger extends horizontally from the ilium pin and terminates in a vertically-oriented pointer. The height and length of the outrigger may be adjusted such that the vertical pointer touches a predetermined spot on the femur. In this manner, the lateral offset may be measured (by adjusting the height) and the length may be measured (by adjusting the length). However, one drawback to the Chan device is that if the anchor pin is not perfectly aligned with the axis of the femur, then reproducing the exact alignment of the femur with respect to the ilium can be difficult. Moreover, locking the movable outrigger into position once a measurement has taken place undesirably requires additional tools.
What is needed, therefore, is a device that assists in bone positioning measurements that is relatively easy to use. A further need exists for such a device that is capable of performing both bone length and lateral offset measurements.
The present invention addresses the above needs as well as others through a device that attaches to an anchor and facilitates accurate and repeatable offset and length measurements.
A first embodiment of the present invention is an apparatus for use in an arrangement for measuring the relative position of two bones during surgery. The apparatus includes a spring-biased clamp and a measurement arm. The spring biased clamp has first and second opposing clamping surfaces that adapted to engage and secure the clamp to an anchor in a fixed vertical position. The anchor is secured to a first bone location. The measurement arm comprises an elongate portion and a locator portion. The locator portion extends angularly from the elongate portion. The measurement arm is slidably supported on the spring biased clamp.
Accordingly, the above-described embodiment employs a spring-biased clamp for fixing the device to an anchor. The use of the spring-biased clamp, among other things, increases convenience of use by eliminating or reducing the need for additional tools to either secure or remove the device.
A second embodiment of the invention is also an apparatus for use in an arrangement for measuring the relative positioning of two bones during surgery. In the second embodiment the apparatus includes a clamp and a measurement arm. The clamp is adapted to engage and secure to an anchor in a fixed vertical position, the anchor being secured to a first bone location. The measurement arm comprises an elongate portion and a locator portion that extends angularly from the elongate portion. The measurement arm is slidably supported on the clamp. The measurement arm is further rotatably supported on the clamp via a spring biased clamping element.
Similar in some respects to the first embodiment, the second embodiment employs a spring biased clamp. However, in this embodiment the spring biased clamping mechanism secures the rotational position of the measurement arm. Such a device allows for rotational movement of the measurement arm, which increases the adaptability of the device, while incorporating the convenience of a spring-biased clamp.
Yet another embodiment of the present invention is an apparatus for use in an arrangement for measuring the relative position of two bones during surgery that also includes a clamp and a measurement arm. The clamp is adapted to engage and secure to an anchor in a fixed vertical position, the anchor being secured to a first bone location. The measurement arm comprises an elongate portion and a locator portion that extends angularly from the elongate portion. The measurement arm is slidably supported on the clamp. The measurement arm is further rotatably supported on the clamp at a position in which an axis of rotation of the measurement arm is spaced apart from a longitudinal axis of the anchor.
The above describe features and embodiments, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings.